The last I read (who the hell knows) from CDC, was that now they “think” that wuflu cannot be spread by an asympotamic person. If that is accurate, that would mean someone went to that event who had symptoms. Unless of course it was spread in a more insidious way.
Only someone very evil would have gone to that even with symptoms.
I really believe that if nothing is coming out of you, no sneezing, no coughing, no runny nose, it’s extremely unlikely you’d infect anybody else.